1. Field of the Invention
The present invention relates to a novel process for preparing polyester-based polymers. More particularly, the present invention relates to a novel and advanced process for preparing polyester-based polymers by using a composite polymerization catalyst which was prepared by reacting titanium compounds and cobalt compounds in the solution containing at least one alcohol.
2. Description of the Background Art
Polyester-based polymers, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and/or polyethylene naphthalate (PEN), which are currently industrially manufactured, have high degrees of crystallinity, higher softening points and numerous other superior properties in terms of mechanical strength, resistance to gas permeability, chemical resistance, thermal resistance, weather resistance and electrical insulation, etc. Thus, they are widely used for manufacturing high quality films, bottles, high strength fibers and other industrial materials.
There are two steps in industrial preparations of polyesters such as PET and/or PEN. The first step is to make esterified low molecular weight compounds by reacting diacid or derivatives of diacid with glycols. The product of this step in making PEN is bis(beta-hydroxyethyl)naphthalate or their low molecular weight prepolymers (hereinafter referred to as xe2x80x9cesterified compoundsxe2x80x9d). The product of this step in making PET is bis(beta-hydroxyethyl)terephthalate or their low prepolymers.
The first step is performed by means of either a direct esterification or an ester-interchange reaction which is called as transesterfication also. In the ester-interchange reaction, dimethyl terephthalate (DMT) or 2,6-naphthalene dicarboxylic acid dimethylester (2,6-NDC) is reacted with ethylene glycol (EG) in the presence of a catalyst such as zinc acetate [Zn(OAc)2] or manganese acetate [Mn(OAc)2] at reaction temperatures ranging from 180 to 260xc2x0 C. and the side product, that is methanol, is removed. In case of direct esterification reaction, TPA (terephthalic acid) or 2,6-naphthalene dicarboxylic acid (2,6-NCDA) is mixed with ethylene glycol (EG) and reacted at the temperatures ranging from 200xcx9c280xc2x0 C. under atmospheric pressure or under slight pressure and the side product, that is water, is removed. Thereafter in the second step, the synthesized, esterified compounds are polycondensed in the presence of a polymerization catalyst such as antimony trioxide (Sb2O3) at higher reaction temperatures ranging from 280 to 300xc2x0 C. under reduced pressure (generally less than 1.0 torr) in order to prepare the high molecular weight polymers.
Currently, in the case of PET, the direct esterification method is mostly used, which uses the TPA as a starting material. But in the case of preparing PEN, because of the high cost, the ester-interchange reaction method is mostly adopted. Meanwhile, PBT can also be prepared by a similar method except that 1,4-butanediol is used instead of EG.
Generally, a reaction catalyst is employed to accelerate and smoothly advance a reaction in preparing polyester. These catalysts include a variety of metal compounds of antimony, titanium, germanium, tin, zinc, manganese, lead and the like.
However, it is well known that the color and the thermal stability of the resulting polyester, especially, PEN, and the reaction rate considerably depend on the catalysts employed. The reactions for preparing polyester are carried out at high temperatures for an extensive period in the presence of catalysts containing metals. Thus, several undesirable side reactions that result in coloring the polymer product yellow and increasing the amount of diethylene glycol and the concentration of terminal carboxylic groups above their optimum levels are accompanied in preparing high molecular weight polyesters. Yellowish color and excessive amount of diethylene glycol deteriorate the physical properties of the polyester such as the melting point, strength and the like. Therefore, it is important to prepare polyester that can exhibit good color and superior physical properties at a higher reaction rate.
Currently, antimony compounds, especially, antimony trioxide, are mostly used as industrial polycondensation catalysts due to its acceptable catalytic activity and moderate price.
But since antimony trioxide is not solved well in ethylene glycol and in reaction intermediate for preparing polyester, it tends to precipitate during the reaction and it cause the resulting color of the polyester to become gray or yellow-green and less transparent. These effects are more distinct when the amount of the catalyst added is increased or the reaction temperature is raised to improve the production rate.
In order to overcome the above-mentioned problems, there have been several methods using catalysts to produce polyester exhibiting good color and superior physical properties by reducing the esterification reaction time and the polycondensation reaction time. However, many of the proposed methods could not overcome the above-mentioned problems: a method of using catalyst as a solution prepared by dissolving antimony trioxide with cobalt compound and phosphorous compound together in ethylene glycol (Japanese Laid Open Patent Publication No. 53-51295) and a method in which a compound of antimony is used with an organic acid (Japanese Laid Open Patent Publication No. 60-166320) were attempted. However, these methods fail to reduce both the esterification reaction time and the polycondensation reaction time. And they also caused several problems in the physical properties of the prepared polyesters in that the color of the prepared polymer is light yellow and the content of diethylene glycol or terminal carboxylic groups is not reduced sufficiently.
Also, as a method to improve the color and physical properties of the prepared polymer, there have been known a method in which compounds of cobalt and alkali metal are used with a compound of antimony (Japanese Laid Open Patent Publication No. 58-117216), a method in which a compound of antimony is used with a compound of tin (Japanese Laid Open Patent Publication No. 49-31317), and a method in which antimony compound, tin compound and compounds of cobalt and alkalimetal, phosphorous compounds are used together (Japanese Laid Open Patent Publication No. 62-265324). However, these methods are incapable of improving the color and transparency, physical properties of the prepared polymer significantly. And these methods fail to provide any important advantage in reducing the reaction time.
Meanwhile, by previous inventions made by the present inventors, problems of preparing polyesters, especially PET, have been overcome by using titanium compound and antimony compound together (U.S. Pat. No. 5,286,836) or by using a composite catalyst containing additional tin compound along with titanium compound and antimony compound (U.S. Pat. No. 5,714,570)
However, a marked difference between the preparation of PEN and PET exists. For instance, the reactant, 2,6-NCDA has a lower solubility in EG because of higher molecular weight and smaller crystal size of 2,6-NDCA than TPA. Therefore, it is not possible to feed the slurry prepared by mixing 2,6-NCDA and EG in similar molar ratio as in PET preparation (generally, EG/TPA=1.1xcx9c2.5) into the reactor.
Since the naphthalene ring structure of 2,6-NDCA or 2,6-NDC is more liable to become colorized by impurities than the benzene ring structure of PET, careful selection of catalyst is very critical to attain good colored product. And because PEN has a higher melt viscosity, it requires a higher polymerization temperature than PET. However, higher temperature makes PEN be colored and more liable to degradation. To overcome this problems, efficient catalyst is essential to reduce the reaction time in preparing the polymer
Although several methods to overcome these problems have been proposed, those were not so successful in shortening the reaction time or in improving the product quality.
Therefore, an object of the present invention is to provide a process for preparing polyester-based polymers while reducing both the esterification time and the polycondensation time and providing good color and excellent physical characteristics to prepare a high quality polyester with high productivity, by reacting a cobalt compound and a titanium compound in the presence of at least one alcohol solvent and using the resultant compound as a catalyst.
The present invention provides a process for preparing polyester polymers comprising the steps of:
(a) esterifying naphthalene dicarboxylic acid (NDCA) or a dicarboxylic acids containing NDCA or ester derivatives thereof, and ethylene glycol or glycols containing ethylene glycol or derivatives thereof to produce esterified compounds or its low molecular weight polymers; and
(b) continuously polycondensing the resultant esterified compounds of step (a) to produce polyester polymers;
wherein in the above preparation process a composite polymerization catalyst is used, which composite polymerization catalyst is prepared by reacting cobalt compounds and titanium compounds in the presence of a solution comprising at least one alcohol compound. The titanate compounds are represented by formula I and selected from the group consisting of a titanate compound, a phosphite complex compound thereof and a mixture thereof:
(RO)4Tixe2x80x83xe2x80x83Formula I
wherein each R is independently the same or different and is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, acetylisopropyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, octadecyl, stearyl, allyl, 2,2-diallyloxymethylbutyl, cyclopentyl, cyclohexyl, naphthyl, phenyl, benzyl, and dodecylbenzyl.
In the present invention, the titanium compound may be a titanium phosphite complex compound represented by the below formula II:
(RO)4Ti.2XP(O)(ORxe2x80x2)2xe2x80x83xe2x80x83Formula II
wherein each of R and Rxe2x80x2 is independently the same or different and is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, acetylisopropyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, octadecyl, stearyl, allyl, 2,2-diallyloxymethylbutyl, cyclopentyl, cyclohexyl, naphthyl, phenyl, benzyl, and dodecylbenzyl and X is selected from the group consisting of hydrogen, halogen, alkyl, alkoxy or aryloxy.
In formula II, Rxe2x80x2 is preferred to be an aromatic group, and more preferably, it forms a complex with an aromatic phosphite such as diphenylphosphite, triphenylphosphite or phenylnaphthylphosphite.
The titanium compound used in the composite catalyst of the present invention can be selected preferably from the group consisting of tetraisopropyl titanate, tetrabutyl titanate, tetraisopropyldi(dioctyl)phosphito titanate and tetraoctyl(ditridecyl)phosphito titanate. Example of other titanium compounds that can be used in the present invention are titanium ethylene glycoxide, titanium halides such as titanium tetrachloride, titanium esters such as potassium titanium oxyoxalate, monoalkoxy titanates selected from the group consisting of isopropyl triisostearoyl titanate and isopropyl tri(N-ethylenediamino)ethyl titanate, titanate chelate compounds selected from the group consisting of dicumylphenyl oxoethylene titanate and di(dioctyl)phosphato ethylene titanate, neoalkoxytitanate compounds selected from the group consisting of neopentyl(diallyl)oxytri(N-ethylenediamino) ethyltitanate and neopentyl(dially)oxytridodecylbenzene sulfonyltitanate, and heterocyclic titanates selected from the group consisting of cyclo(dioctyl) pyro-phosphatodioctyl titanate and dicyclo(dioctyl) pyrophosphatotitanate.
The cobalt compound used in the composite catalyst of the present invention can be selected from the group consisting of cobalt acetate, cobalt acetylacetonate, cobalt bromide, cobalt carbonate, cobalt chloride, cobalt 2-ethylhexanoate, cobalt fluoride, cobalt hydroxide, cobalt nitrate, cobalt oxalate, cobalt perchlorate, cobalt sulfate, cobalt tetrafluoroborate and cobalt thiocyanate.
Almost all primary alcohols can be used in the preparation of composite catalyst of the present invention. That is, one or the mixture of the alcohols selected from the group consisting of a primary alcohol, a secondary alcohol, a polyhydric alcohol and mixtures thereof can be used. For example, a primary alcohol can be selected from aliphatic, cyclic or aromatic alcohols having 1 to 20 carbons. More particularly, primary alcohols can be selected from methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-amyl alcohol, acetylisopropyl alcohol, pentyl alcohol, hexyl alcohol, heptyl alcohol, 2-ethylhexyl alcohol, octyl alcohol, decyl alcohol, dodecyl alcohol, tridecyl alcohol, octadecyl alcohol, stearyl alcohol, allyl alcohol, 2,2-diallyloxymethylbutyl alcohol, cyclopentyl alcohol, cyclohexyl alcohol, phenyl alcohol, benzyl alcohol and dodecylbenzyl alcohol. Among those alcohols, it is more preferable to use an alcohol selected from methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, pentanol, hexanol, 2-ethylhexyl alcohol, octanol and isooctanol.
The secondary alcohol can be an aliphatic, cyclic or aromatic alcohol selected from ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1.3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-haxanediol, 1,4-cyclohexane dimethanol, 2,6-decahydronaphthalene dimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol S, bishydroxyethoxy bisphenol A, and tetrabromobisphenol A. Especially, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1.3-propanediol and 1,4-butanediol are preferred among them. Also, a polyhydric alcohol such as trimethylolpropane, glycelin, pentaerythritol can be used.
Any alcohol or the mixture of alcohols which does not slow the reaction rate or degrade the physical quality of the polymer can be used. But it is preferable to use an alcohol that is less expensive and more effective in reacting cobalt compounds and titanium compounds.
When the composite catalyst is prepared in alcohol solution, the reaction conditions are not necessarily restricted. But composite catalyst solution reacted at a temperature of 30xc2x0 C.xcx9c300xc2x0 C., preferably at 50xc2x0 C.xcx9c200xc2x0 C., under atmospheric pressure is more desirable due to its higher activity in make polyester polymer. Required reaction time is 0.1-10 hrs, 0.5-6 hrs preferably.
The amount of alcohol used in the preparation of composite catalyst need not be restricted. However, it is preferred to use the amount of alcohol to make the concentration of titanium compounds and cobalt compounds to be about 0.1 to 50 wt %, more preferably about 0.1 to 10 wt %. According to the kinds of alcohol and according to circumstances, the catalyst is separated as a solid or powder. The separated powder also can be used as a reactive catalyst with its excellent catalytic effect.
If nothing interferes with the reaction, alcohol can be used in a mixed solution with a different solvent, and especially, water may be added to alcohol. In case of adding water, preferred amount of water to be added is 0.01 to 10.0 times of the alcohol used. And most preferably, 0.1 to 1.0 times of the alcohol is added.
Meanwhile, the above processed catalyst composition may be combined together with antimony compounds and/or tin compounds.
Antimony compounds usable in the present invention can be selected from the group consisting of antimony oxides such as antimony trioxide, antimony tetroxide or antimony pentoxide, antimony halides such as antimony trichloride or antimony trifluoride, antimony carboxylates such as antimony triacetate [Sb(OAc)3), antimony tristearate, antimony tribenzoate, antimony tri-2-ethylhexanoate, or antimony trioctoate, antimony compounds combined with ether such as antimony triethoxide, antimony ethylene glycoxide, antimony tri-isopropoxide, antimony tri-n-butoxide, or antimony triphenoxide, antimony hydroxide, and antimony sulfide. Among these antimony compounds, antimony trioxide and antimony triacetate are preferred.
Alternatively, a tin compound represented by formula III can be used in the preparation of the present composite catalyst:
xe2x80x83R2SnXxe2x80x2xe2x80x83xe2x80x83Formula III
Wherein R2 is identical to the R of the above-mentioned titanium compounds of formula I and II, and Xxe2x80x2 represents oxygen, sulfur, halogen or the compounds containing ether, thio or ester bonds. More specifically, tin compounds usable in the present invention include dibutyltin oxide, diphenyltin sulfide, dimethyltin chloride, dibutyltin sulfate, dioctyltin mercaptide, dibutyltin bis(dibutyldithiocarbamate), dibutyltin laurate, dibutyltin disalicylate, dibutyltin maleate, dibutyltin methoxide, dibutyltin laurate maleate, dibutyltin stearate, dioctyltin bis(isooctylmercaptoacetate), dioctyltin maleate and dibutyltin mercaptoacetate.
It is not necessary to limit the amount of the catalyst used in the present invention. However, it is desirable to have enough quantity to obtain desirable reaction rates depending on the reaction condition. The desirable quantity of the composite catalyst is 20 to 2000 ppm, more preferably 50 to 500 ppm of the resulting PEN polymer.
Also, the catalyst can be added to the reaction mixture during the esterification reaction period or some time between esterification reaction and polycondensation reaction.
However, it is desirable to add the composite catalyst before or at the beginning of the esterification reaction to shorten the both esterification reaction time and polycondensation time. Especially when the esterification reaction is performed by using the premixed slurry of 2,6-NDCA or TPA with ethylene glycol, it is preferable to add the present novel composite catalyst to the reactant slurry before esterification reaction. Alternatively, the composite catalyst can be added in two times. In that case about 50 wt % of required composite catalyst is added before esterification reaction and the rest is added before the initiation of polycondensation reaction.
When performing the direct esterification reaction according to the present invention, it is desirable to perform the reaction at 200xcx9c280xc2x0 C. at any pressure condition such as atmospheric or high pressure condition. In the case of the ester interchange reaction, it is desirable to use the composite catalyst of the present invention instead of the conventional catalyst at 180xcx9c260xc2x0 C.
The esterified compounds obtained by the esterification reaction can be polycondensed at 280xcx9c300xc2x0 C., preferably having a final temperature of 285xcx9c295xc2x0 C. It is desirable to have lower than 1 torr of vacuum as a final pressure, and it is desirable to elevate the reaction temperature and to slowly increase the degree of vacuum simultaneously during the polycondensation reaction.
Also it is possible to use other reaction catalysts together with the composite catalyst of the present invention. Germanium compounds such as germanium oxide, carboxylate compounds of zinc or manganese or lead such as zinc acetate, manganese acetate and lead acetate, and alkali metal compounds such as sodium hydroxide, potassium hydroxide, and sodium acetate, potassium acetate can be used.
The present invention can be effectively applied in producing polyester polymers and/or copolymers by esterifying dicarboxylic acid or derivatives selected from the group of naphthalene dicarboxylic acid (NDCA), dicarboxylic acid containing NDCA or derivatives thereof, especially, 2,6-NDCA, TPA, 2,6-NDC, DMT and their mixtures with glycol and derivative thereof selected from the group of ethylene glycol, 1,3-propanediol, 1,4-butanediol and their mixtures.
In addition, the present invention can also be effectively applied in producing other aliphatic or aromatic polyester and their copolymers by using other dicarboxylic acids or their esters and various glycols beside ethylene glycol.
Usable dicarboxylic acid are one or the mixture of selected from the group of aromatic or aliphatic, cyclic dicarboxylic acid and derivatives thereof such as phthalic acid or isophthalic acid, diphenylsulfondicarboxylic acid, diphenylmethanedicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid and decalindicarboxylic acid, or the derivatives thereof such as methyl ester, ethyl ester and phenyl ester compounds.
The usable glycols include aliphatic, cyclic and aromatic diols such as 1,3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-haxanediol, 1,4-cyclohexane dimethanol, 2,6-decahydronaphthalene dimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol S, bishydroxyethoxy bisphenol A, and tetrabromobisphenol A.
Also, a polyfunctional cross-linking agent selected from the group consisting of trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol, and/or a terminating agent selected from the group consisting of monomethoxypolyethylene glycol, stearyl alcohol, palmitic acid, benzoic acid, and naphthoic acid can be added.
Moreover, a phosphorous compound can be added as a thermal stabilizer. The phosphorous compounds that can be used as a thermal stabilizer are phosphoric acid, phosphorous acid, metaphosphoric acid, trimethylphosphate, triethylphosphate, triphenylphosphate, trioctylphosphate, dimethylphosphite, diethylphosphite, dicyclohexylphosphite, diphenylphosphite, dioctylphosphite, dimethylpyrophosphate, diethylpyrophosphate, diphenylpyrophosphate, dicyclohexylpyrophosphate, dioctylpyrophosphate. A hindered phenol such as Irganox 1010, Irganox 1076, and Irganox 1098, products of Ciba-Geigy Company, Germany, can be added as an antioxidant. In case of employing titanate compounds in the phosphite complex form having the formula II, it is not necessary to add such stabilizer.
In addition, other additives can be used: an ultraviolet absorbent such as benzotriazol, an anti-softening point dropping agent such as triethylamine, a delustering agent such as titanium oxide, a nucleating agent such as silica and alumina, and other compounds such as a dye, a fluorescent whitening agent, an antistatic agent and a flame retardant.
The present invention will now be described with the following examples. It should be understood that these examples are intended to be illustrative manner only and the present invention is not limited to the conditions, materials or devices recited therein.
In the following examples, all parts are given by weight unless otherwise stated. Esterification Ratio (ER) was obtained by measuring the acidity value (AV) and saponification number (SN) of the produced esterified compound after the esterification reaction. The intrinsic viscosity (xcex7) of the polymers was evaluated by measuring the dilute polymer solution prepared by dissolving the polymer in an admixed co-solvent of phenol and tetrachloroethane. The color of the polymers was measured in the chip state of the polymers by color diffractometer, and the L values and b values describe the lightness and the degree of yellowness of the polyesters, respectively. A higher L value and a lower b value indicate improved color.